1. Field of the Invention
An embodiment of the present invention relates to a ring oscillator for a temperature sensor, a temperature sensor circuit, and a semiconductor device having the same, which may include a ring oscillator for a temperature sensor which can accurately detect a substrate temperature by using an oscillation frequency that depends greatly on a substrate temperature, a temperature sensor circuit, and a semiconductor device having the same.
2. Description of the Related Art
In a semiconductor device, temperature of its semiconductor substrate (or substrate temperature) is raised by its own operation. The rise in the substrate temperature may cause a malfunction or may eventually invite thermal runaway. Accordingly, the substrate temperature needs to be measured accurately.
For example, it is known that the substrate temperature is measured by using a drain-substrate leakage current of a MISFET (see Japanese Patent Laid-Open No. 54-073580). It is also known that the substrate temperature of a power semiconductor device is measured by using a current flowing in a bipolar transistor (see Japanese Patent Laid-Open No. 6-077409). Further, it is known that the substrate temperature is measured by using a difference of voltage potential in a series circuit including a semiconductor diode and resistor (see Japanese Patent Laid-Open No. 2004-134472).
Incidentally, it is known that an oscillation frequency of a ring oscillator is controlled based on a value of a leakage current at a leakage current generating unit including a pn junction (see Japanese Patent Laid-Open No. 5-175793).
By the above known technique to measure the substrate temperature, it is possible to accurately measure the substrate temperature to certain degree, and to prevent a malfunction and the like of the semiconductor device. However, an increasing of scale integration in a semiconductor device invites an increasing of an amount of heat generated by the semiconductor device. Then, the substrate temperature needs to be measured more accurately. For this reason, it is necessary to measure a factor having a higher dependence on the temperature than that of a current or voltage, which is obtained as a result of the measurement in the well-known technique to measure the substrate temperature.